A great variety of transducers exist in the art that are used to measure force and pressure in different environments. Many of these sensors use piezoresistive, piezoelectric, and capacitive methods for measuring force and pressure. All these transducers produce relatively low level analog signals wherein both the zero pressure reading and the scale factor can vary as a function of temperature to one degree or another. Moreover, to obtain a digital signal from such a device requires a conversion of the analog to a varying frequency. The consequences of this conversion are less precise force or pressure transducers.
On the other hand, transducers that rely on vibrating structures for the measurement of physical properties such as pressure and force have a number of advantages over conventional analog transducer structures. Vibrating beam transducers are well known in the art. For example, commonly-assigned U.S. Pat. No. 5,473,944, entitled “Beam Pressure Sensor Employing Dielectrically Isolated Resonant Beams and Related Method of Manufacture” issued Dec. 12, 1995 to Kurtz, et al., and U.S. Pat. No. 5,543,349, entitled “Method for Fabricating a Beam Pressure Sensor Employing Dielectrically Isolated Resonant Beams” issued Aug. 6, 1996 to Kurtz, et al., disclose pressure transducers that measure the change in vibration of resonating beams to determine an applied pressure.
In the conventional vibrating beam transducers disclosed in the above referred to patents, as a force is applied to a diaphragm, the diaphragm deflects in response to the applied force and presses on, contacts or otherwise causes a pressure to be imposed on a vibrating beam. The beam is typically vibrating at a resonant frequency, which is altered in response to the deflecting diaphragm. The change in frequency of the vibrating beam is representative of the force applied. In the case of a dual resonating beam transducer, the change in frequency of one beam with respect to a second beam is used to generate a beat frequency that may be used to precisely measure the applied force. For example, if one can resolve the frequency to one part in 105 and each natural frequency is on the order of 100 kHz and the difference in frequency is 10 kHz, an enhancement in the precision of the measurement by a factor of 10 will be achieved.
However, in these conventional transducers it is difficult to measure a precise variation of the resonant frequency as the change in beam resonant frequency depends on the ability to transmit the force from the diaphragm to the vibrating beam. Hence, while a precise measurement may be obtained by the change in resonant frequency, it may not be an accurate measurement.
Accordingly, there is a need in the industry for a resonant or vibrating transducer that provides a more accurate measure of the applied force.